Drum mixers for manufacturing asphaltic compositions out of an aggregate material are known in the art. An aggregate material known as "recycled asphaltic pavement" (RAP) is an inexpensive and plentiful aggregate material which can be used to manufacture an asphaltic composition. The RAP material is formed from a mixture of an asphaltic material, aggregates and mineral binder or "fines".
Virgin aggregates can also be used in manufacturing asphaltic compositions. As the virgin aggregate flows through the drum mixer, it is combined with liquid asphalt and fines to produce the asphalt composition. However, producing an asphaltic composition from virgin aggregate is more expensive than producing the asphaltic composition from RAP material because the virgin aggregate is more costly than the RAP material, and more asphaltic material must be added to the virgin aggregate.
When RAP material has been used in previous drum mixers, the RAP material was introduced into the drum mixer in a different location separate from the virgin aggregate to minimize what is known in the art as "blue smoke" and also to not degrade the RAP material. And, as a practical matter, the ratio of RAP material which could be used relative to virgin aggregate was about 25% with maximums up to 50% in some cases. Thus, it has been necessary to use a substantial amount of expensive virgin aggregate in producing the asphaltic composition.
By increasing the ratio of RAP material to virgin aggregate, the costs of manufacturing the asphaltic composition can be significantly reduced. It is to such a drum mixer for manufacturing an asphaltic composition out of a high ratio of RAP material to virgin aggregate material that the present invention is directed.